Amplification from two or more active devices may be classified as multiplicative or additive amplification. In multiplicative amplification, the overall gain is proportional to the product of the gains supplied by the individual modules, while in additive amplification the gain is proportional to the sum of the powers contributed by the individual active devices.
The vast majority of amplifiers makes use of the multiplicative process through cascading. The most prominent exception is the distributed or traveling wave amplifier whose amplifying mechanism is based on the additive principle. See, W. S. Percival, "Thermionic Valve Circuits", British Pat. No. 460 562, Jan. 25, 1937; and E. L. Ginzton, W. R. Hewlett, J. H. Jasberg, and J. D. Noe, "Distributed Amplification", Proc. IRE, Vol. 36, pp. 956-969, August 1948.
While in most practical applications additive amplification produces less gain per device when compared to multiplicative amplifiers, it yields significantly larger bandwidths through the ingenious use of the active devices' parasitics. Since 1937, when the invention of the distributed amplifier was patented, very few modifications of the original concept have surfaced. However, recently two variations have emerged that are of practical importance. In the first, the common source MESFET (MEtal Semiconductor Field Effect Transistor) is replaced by a cascaded two-port that consists of a common source first stage followed by a common gate second stage separated by a two-port that serves as an interstage transformer. See D. E. Dawson, M. L. Salib, L. E. Dickens, "Distributed Cascode Amplifier and Noise Figure Modeling of an Arbitrary Amplifier Configuration", ISSCC Digest, 1984. This type of amplifier produces moderately higher gains and significantly higher reverse isolations.
In the second modification, two distributed amplifier circuits are paralleled by establishing a common drain line. The input signal is divided and applied to the two input terminals of the ensuing network while the output signal is extracted at the common drain terminal. See Y. Ayasli, L. D. Reynolds, R. L. Mozzi, and L. K. Hanes, "2-20 GHz GaAs Traveling-Wave Power Amplifier", IEEE Trans. Microwave Theory Tech., Vol. MTT-32, March 1984. In this case the output power is doubled with no change in gain.
The present invention is a circuit that adds a new dimension to the distributed amplifier in the form of two or more rows of transistors, i.e., active tiers. In its most general form the new amplifier consists of an array of m rows and n columns of active devices. Each column is linked to the next by inductors or transmission line elements connected at the input and output terminals of each transistor, thereby composing a lattice of circuit elements. For m active tiers, there are 2m idle ports that are terminated into power dissipating loads. The purpose of adding the vertical dimension to the horizontal dimension of the distributed amplifier in the form of the m.times.n rectangular array is to combine the multiplicative and additive amplification process in one and the same module. The advantages of this new device include significantly higher gain and reverse isolation over wide bandwidths at considerably reduced size. Due to its regular geometrical arrangement of circuit elements very much similar to the rectangular array of mathematical elements in a matrix, the new device is herein called a matrix amplifier.
It is therefore a primary object of the present invention to provide a microwave amplifier that provides both multiplicative and additive amplification in a distributed amplifier with two or more rows of transistors, i.e., active tiers.